Changes on the earth’s surface

1. Changes on the earth’s surface 1-3

2. I. Weathering • Weathering – breakdown of rock at or near the earth’s surface into smaller and smaller pieces • MechanicalWeathering – occurs when rock is actually broken or weakened physically • 1. breaks large masses of rock into smaller pieces (boulders, • stones, pebbles, sand, silt, and dust)

3. C. ChemicalWeathering – alters a rock’s chemical makeup by changing the minerals that form the rock or combining them with new chemicals • 1. can change one rock into a completely different type of rock • 2. many caves are formed when acidic water seeps into cracks of • rocks • 3. acid rain – chemicals in the polluted air combine with water • vapor and fall back to earth (destroys forests, pollutes water, eats away at stone buildings)

4. examples Mechanical Weathering Chemical Weathering

5. II. erosion • Erosion – movement of weathered materials such as gravel, soil, and sand • 3 most common causes of erosion: • 1. water • 2. wind • 3. glaciers • Important part of the cycle that has made and kept the earth a place where living things can survive

6. A. Water • Water is the greatest cause of erosion, because over time, water can cut into the hardest rock and wear it away • Water moving down a streambed carries sediment (small particles of soil, sand, and gravel)…that sediment helps grind away the surface of rocks • The rock and soil that is carried away with erosion eventually creates other landforms • The Mississippi River carries approximately 159 million tons of sediment a year • Crashing ocean surf causes steep bluffs, cliffs, or sand dunes

7. B. Wind • Cause of erosion in areas where there is little water and few plants to hold the soil in place • In the Great Plains, the rich fertile soil that they once had was blown away by the wind during a drought…this area is now known as the “Dust Bowl” because they cannot grow anything there anymore • The wind can also deposit mineral-rich dust and silt called loess, which can help areas that once were barren • Sandstorms can cause erosion by carving or smoothing the surfaces of rock formations and man-made objects

8. C. glaciers • Glaciers – huge, slow-moving sheets of ice • Form over many years as layers of unmelted snow are pressed together, thaw slightly, and then turn to ice • As glaciers move, they carry dirt, rocks, and boulders • The time periods where much of the earth is covered in glaciers are known as Ice Ages – geologists believe that we’ve had at least 4 • Much of the U.S. was formed by glaciers (Great Lakes, Long Island, etc.) • Glaciers slide forward because of how heavy they are and only pieces of it move at a time (oozes)

9. glaciers